Japan's antitrust watchdog on Wednesday raided the offices of Rakuten Inc. and two other online booking operators, alleging they hurt fair trade by requiring accommodation providers to offer their lowest prices on their platforms, according to a source close to the matter.

The Fair Trade Commission's probe comes amid its closer scrutiny of allegedly obscure business transactions involving providers of digital platforms and the sale of products and services via search engines and e-commerce sites, among other avenues.

According to the source, Tokyo-based Rakuten, U.S. firm Expedia Group Inc. and Dutch outfit Booking.com B.V. have for several years allegedly urged clients to set accommodation prices the same as, or lower than, those offered on rival websites and on hotels' official sites.